Peptides are polymers formed by linking amino acids with amide bonds. Peptides play various roles in a biological system. For example, peptide hormone is the largest group of hormones which modulate various biological processes in biological subjects. One nanogram of hyrotropin-releasing hormone injected into a mouse increases the uptake of iodide from the blood into the thyroid gland (R.L. Kisliuk, Principles of Medicinal Chemistry, 4th Ed., W.O. Foye, et al. Eds., Williams & Wilkins, 4th Ed. 1995, p. 606). Tuftsin (Thr-Lys-Pro-Arg (SEQ ID NO: 6)) stimulates phagocytosis and promotes antibody-dependent cellular cytotoxicity (V.A. Najjar, Mol. Cell. Biochem. 41, 1, 1981). Met-enkephaline (Tyr-Gly-Gly-Phe-Met (SEQ ID NO: 1)) isolated from brain and small intestine, acts as morphine does, in that it binds to the same receptor and has analgesic activity (J.R.Jaffe and W.R. Martin, in Pharmacological Basis of Therapeutics, A.G. Gilman, et al., Eds., New York, Pergamon Press, 1990, p. 481). Other examples of peptide hormones include, without limitation, oxytocin (Pierce et al., J. Biol. Chem. 199, 929, 1952), vasopressin (Kamm et al., J. Am. Chem. Soc. 50, 573, 1928), angiotensin (J.C. Garrison and M.J. Peach, in Pharmacological Basis of Therapeutics, A.G. Gilman, et al., Eds., New York, Pergamon Press, 1990, p. 749), gastrin (P.C. Emson and B.E.B. Sandberg, Annu, Rep. Med. Chem., 18, 31, 1983), somatostatin (A.V. Schally, et al., Annu. Rev. Biochem., 47, 89, 1978), dynorphin (M.G. Weisskopf, et al., Nature, 362, 423, 1993), endothelin (A.M. Doherty, J. Med. Chem., 35, 1493, 1992), secretin (E. Jorper, Gastroenterology, 55, 157, 1968), calcitonin (M.V.L. Ray, et al., Biotechnology, 11, 64, 1993), insulin (F. Sanger, Br. Med. Bull., 16, 183, 1960), and competence stimulating peptide (CSP).
Another group of peptides are anti-microbial peptides which have been found to participate in innate immunity in a wide variety of organisms (Reddy et al. 2004). These peptides and others have attracted much interest due to their potential usefulness in treating infections, especially because they are often effective against bacterial strains that have become resistant to conventional antibiotics. One well-known class of anti-microbial peptides is the tachyplesins. Another class of anti-microbial peptides is histatin peptides and the derivatives. Another class of antimicrobial peptide is hepcidin, which is also referred as LEAP-1, for liver-expressed antimicrobial peptide.
Another group of peptides are calcium binding peptides that bind specifically to calcified surfaces. One example of a calcium binding peptide comprises three amino acid repeat sequence (X-Y-Z)n, wherein X is aspartic acid, glutamic acid, asparagine, alanine or glutamine, Y and Z are alanine, serine, threonine, phosphoserine, or phosphothreonine, and n is a number from 1 to 40.
Unfortunately, peptides and peptide related compounds are rapidly proteolysized by proteolytic enzymes. When peptides and peptide related compounds are taken orally, they will be proteolysized in a few minutes. Other systematic administrations of peptides and peptide related compounds are painful, and in many cases require frequent and costly office visits to treat chronic conditions.
Therefore, a need exists in the art for novel compositions that are capable of being delivered efficiently and effectively to the action site of a condition (e.g., a disease) to prevent, reduce or treat conditions as well as minimize adverse side effects.